Imaging systems often include fixed geometries that are used to scan objects of various dimensions and characteristics in a variety of different imaging scenarios. Such systems, however, may not be optimized for specific patients and imaging requirements, often resulting in decreased sensitivity and resolution. The decrease in sensitivity, in turn, translates into higher radiation dosage for a subject or sub-optimal imaging. Accordingly, currently available imaging systems sub-optimally distribute the exam scan time and/or employ prolonged scans to acquire adequate imaging statistics. Such exams, however, compromise patient comfort and often result in image artifacts caused by patient motion, in turn, leading to inaccurate diagnoses.
Recent advances in imaging system design aim to reduce scan intervals, or alternatively, the radiation dose administered to the patient by using new and improved components such as detectors and collimators. Certain imaging systems, for example, include custom detector geometry, innovative collimation designs including multiple pinhole or slit-hole collimators and use of solid-state detectors for improving diagnostic imaging processes. Particularly, adaptive imaging systems allow for autonomously altering data-acquisition configurations or protocols in near real time for improving image reconstruction.
Adaptive imaging, in particular, aims to optimize one or more of the system parameters in near real time for reducing radiation dose while simultaneously improving image quality over conventional implementations. A conventional single photon emission computed tomography (SPECT) system, for example, typically employs a uniform scan speed, which determines the time that a detector remains at a specific view angle for acquiring “counts” or gamma emission events. The acquired data, however, can vary significantly from one view to another owing to characteristics of the particular region of interest (ROI) being imaged, a view angle, attenuation and finite collimator resolution. Accordingly, the gamma radiation emanating from one particular view angle can have an effective count rate that is different from the effective count rate at another view angle. In a SPECT implementation using a uniform scan and a specified total scan interval, the time spent by the detector at each view angle, thus, may be longer or shorter than appropriate to gather sufficient projection data for generating the PET or SPECT image of a desired spatial resolution.
Accordingly, some present day systems are known to employ certain adaptive imaging techniques for improving diagnostic scanning. By way of example, recent research on adaptive imaging protocols entail use of derived expressions for the performances of ideal linear observers and linear estimators. Certain other techniques are drawn to adaptive zoom-in positron emission tomography (PET) systems with an insert placed into a PET scanner for imaging a small field of view in high resolution. Furthermore, most of the recent techniques for improving image quality metrics require ‘a priori’ knowledge of the lesion or tumor being imaged, which is typically determined from the reconstruction of scout data.